1. Field of the Invention
This invention relates to semiconductor material processing and, in particular, to the etching of semiconductor materials.
2. Art Background
Removal techniques, e.g., etching and cleaning, are universally practiced on semiconductor materials, metal materials, and/or dielectric materials in the production of electronic devices and/or materials. Because of the importance of these procedures, extensive research has been expended in improving established techniques and developing novel approaches. Through this research, processing times have been significantly diminished, and the quality of these processes has been substantially improved.
One approach that has been used for decreasing processing times is the simultaneous treatment of a plurality of substrates, e.g., semiconductor substrates or semiconductor substrates that have been processed and that have various levels including metal, semiconductor, and/or insulator regions. A significant problem, however, occurs when a plurality of substrates is treated. (Substrates, for the purpose of this invention, comprehend any body upon which a device is fabricated, including, but not limited to, devices in process, substrates utilized in semiconductor device fabrication, and substrates utilized in the manufacture of hybrid integrated circuits.) This problem, denominated the loading effect, is characterized by a change in removal characteristics produced by the presence of a substrate area significantly larger than that of a single substrate, i.e., the presence of several substrates. The loading effect often is manifested both locally and globally. The local loading effect leads to non-uniformities across each substrate. For example, in integrated circuit fabrication, often more material at the periphery of a substrate is removed than at the center of the substrate with a concomitant unacceptable non-uniformity.
In the global loading effect, all substrates of a batch are etched at the same rate and yet this rate differs from the rate achieved when a different number of substrates is treated. This effect is quite disadvantageous since the etching conditions must be adjusted or the time varied for the particular number of substrates that is to be treated. The result of each loading effect is either a significant increase in processing time, and thus expense, or the production of substrates that are unacceptable for electronic devices.
Since the processing of a plurality of substrates presents many difficulties, techniques are being employed that are adapted to the processing of individual substrates. For example, excellent etching is produced using species generated in a plasma and directed by electric fields towards the substrate that is immersed in the plasma. Exemplary processes and apparatuses are described in, for example, U.S. Pat. No. 4,383,885, issued May 17, 1983. A second approach that has been utilized and described in Journal of the Electrochemical Society, 129, S. Dzioba et al, page 2537 (1982), Proceedings of the 7th Conference of Solid State Devices, Y. Horiike and M. Shibagaki, Tokyo (1975), supplement to the Japanese Journal of Applied Physics, 15, page 13 (1976), and Thin Film Processes, Chapter V-2, C. M. Melliar-Smith and C. J. Mogab, Academic Press, edited by J. L. Vossen and W. Kern, New York (1978) is the separation of the substrate from the region where the etching species is produced. In such a process, a discharge is established in one region and the etching species produced in this discharge is allowed, generally through diffusive and bulk flow processes, to leave the discharge region and to induce etching or cleaning of the substrates in a second, disjoint region. This downstream process has been employed generally to prevent the plasma from damaging the substrate. For example, when a substrate is present in the plasma region, it is subjected to bombardment by kinetically energetic species. These energetic species often induce sputtering of substrate material. The radiation and fields associated with the plasma also have the potential for inducing damage. Despite the reduction of damage to the substrate, attempts to expand downstream removal techniques to multiple substrates have led to loading effects, and thus the techniques presently employed remain, to a large extent, repetitive single substrate methods.